The present invention relates to a hole cutter having a blade cylinder with a rotation axis and a plurality of blade portions, which are arranged along the rotational direction at intervals.
Conventional hole cutters disclosed in Japanese Laid-Open Patent Publication No. 5-42407 and Japanese Laid-Open Patent Publication No. 5-154709 include first and second blade portions, which are adjacent to each other. The first blade portion has two blades (an outside blade and an inside blade) with a stepped cutting edge in between, and the second blade portion has a single blade.
According to the hole cutter of the above publications, the inside blade of the first blade portion is displaced from the edge of the second blade portion along the direction of the rotation axis. This provides a non-cutting portion in the second blade portion, which rarely contributes to cutting operation. Also, the outside and inside blades of the first blade portion divide shavings. Accordingly, divided shavings having different thicknesses are smoothly discharged at different speeds. However, since the shavings are only parted into two strips, the shaving discharge performance is not sufficiently improved.